The present invention relates generally to ground proximity warning systems for use in aircraft. More particularly, the apparatus, methods, and computer program products of the present invention relate to generating a runway field clearance floor envelope about a selected runway for use by a ground proximity warning system to provide appropriate ground proximity warning alerts.
An important advancement in aircraft flight safety has been the development of ground proximity warning systems. These warning systems analyze the flight parameters of the aircraft and the terrain surrounding the aircraft. Based on this analysis, these warning systems provide alerts to the flight crew concerning possible inadvertent collisions with terrain or other obstacles. Further, these ground proximity warning systems ensure that the aircraft maintains a minimum altitude with regard to terrain underlying the aircraft.
For example, one ground proximity warning system has been developed that generates terrain caution and warning envelopes that extend forward of the aircraft based on the position and flight parameters of the aircraft. Terrain and obstacles that pierce the terrain caution and warning envelopes are displayed to the flight crew as potential ground proximity problems by appropriate alarms or warnings. Further, and importantly, the ground proximity warning system also generates terrain clearance floor envelopes that provide minimum altitudes that the aircraft should maintain above terrain underlying the aircraft. If the altitude of the aircraft with respect to the underlying terrain is less than the minimum altitude required by the terrain clearance floor envelope, the ground proximity warning system will provide appropriate alerts.
FIG. 1 illustrates a typical terrain clearance floor envelope 10 generated by at least one ground proximity warning system. The terrain clearance floor envelope is typically generated with reference to a selected runway 12. For different distances from the selected runway, the terrain clearance floor envelope prescribes different minimum altitudes that the aircraft should maintain above terrain currently underlying the aircraft. Beyond some maximum distance 14 from the selected runway, the aircraft must maintain at least some minimum altitude 16 above underlying terrain.
For example, if an aircraft is approximately 5 nm from a selected runway, the terrain clearance floor may prescribe that the aircraft should maintain at least an altitude of 400 ft above terrain underlying the aircraft. As such, if the aircraft is flying over terrain that has an elevation of 5,000 ft, the aircraft should maintain an altitude of at least 5,400 ft. In this example, if the aircraft dips below 5,400 ft altitude, the ground proximity warning system will provide appropriate alerts.
Importantly, with reference to FIG. 1, for distances closer to the selected runway, the terrain clearance floor envelope requires smaller minimum clearance altitudes that the aircraft should maintain above current terrain. This portion of the terrain clearance floor envelope reflects a landing pattern of the aircraft. The altitudes at various distances from the selected runway are selected to provide ground proximity warning protection, while also reducing generation of nuisance alarms that may disrupt the flight crew during landing. For example, when the aircraft is 2 nm from the selected runway, the flight crew will not receive an alert unless the aircraft dips to an altitude that is less than 200 ft above the underlying terrain.
For most instances, the terrain clearance floor envelopes generated by the ground proximity warning system, such as the terrain clearance floor envelope illustrated in FIG. 1, are generally advantageous as they provide ground proximity warning protection, while at the same time reducing nuisance alarms. However, there may be specific instances where additional ground proximity warning protection may be desired.
Specifically, as described above, the terrain clearance floor envelope requires minimum altitudes that the aircraft should maintain above current terrain depending upon the distance between the aircraft and selected runway. While the terrain clearance floor envelope is typically more than adequate for ground proximity warning protection, problems may occur where terrain near the selected runway, (e.g., within 2 to 15nm of the selected runway), is at a significant lower elevation than the elevation of the selected runway or terrain or obstacles in close proximity to the selected runway. In this instance, the current terrain clearance floor envelopes generated by the ground proximity warning system may not provide desired warning time for reacting to these changes in elevation.
Specifically, FIG. 2 illustrates a situation where providing added reaction time to the flight crew of the aircraft may be desired. FIG. 2 illustrates a situation where the elevation of the selected runway 12 or terrain or obstacles proximate to the selected runway are at a significantly higher elevation, (e.g., elevation 800 ft), than terrain 18 less proximate to the selected runway, (e.g., elevation 300 ft). In this situation, it may be desired to provide an increased reaction time to the flight crew of the abrupt change in elevation that occurs near the selected runway.
In particular, with reference to FIG. 2, if an aircraft 8 is more than 15 nm from the selected runway, (see position 20), the aircraft will maintain an altitude above the terrain underlying the aircraft of at least 700 ft to avoid ground proximity alarms. The 700 ft altitude buffer between the aircraft and underlying terrain typically provides desired reaction time for reacting to changes in the elevation of the terrain. However, as the aircraft approaches the selected runway, the minimum altitude that the aircraft must maintain above underlying terrain decreases. As such, when the aircraft is in close proximity to the selected runway, the flight crew will not receive an alert until the aircraft is much closer to the underlying terrain. This reduction of the required altitude above underlying terrain, in turn, reduces the reaction time for the flight crew to react to abrupt changes in elevation.
For example, at 5 nm, (i.e, 4+K), from the selected runway, (see point 22), the aircraft need only maintain an altitude of 400 ft above underlying terrain to avoid generation of alarms. Further, at positions, (see point 24), closer to the selected runway, the terrain clearance floor envelope decreases to even lower altitude requirements for the aircraft to maintain above underlying terrain. These reduced altitude requirements further reduce the reaction time for the flight crew to react to abrupt changes in elevation near the selected runway.
While reduction of the minimum altitude between the aircraft and underlying terrain as the aircraft approaches the selected runway is typically not problematic for most landing procedures, it may be problematic in the above example shown in FIG. 2. Specifically, due to the terrain clearance floor envelope, as long as the aircraft remains at an altitude above underlying terrain that is greater than the altitude defined by the terrain clearance floor envelope, the aircraft can continue to descend as it approaches the selected runway without generating alarms concerning the altitude of the aircraft. As such, if there is an abrupt upward change in the elevation of terrain in close proximity to the selected runway, (see point 25), the flight crew may not receive an alert from the terrain clearance floor envelope until the aircraft is within the range of 10 to 100 ft above the terrain, depending on distance to the selected runway. In this instance, the alert provided by the ground proximity warning system may not provide the flight crew with a desired time to react to the change in elevation. Specifically, the flight crew may have to maneuver the aircraft in an abrupt fashion to avoid the terrain, which may be unsettling to the flight crew and possibly the passengers on the aircraft.
One solution to the above problem may be to increase the minimum altitudes defined by the terrain clearance floor envelope for distances closer to the selected runway. However, this is somewhat problematic as it may increase the generation of nuisance alarms in those instances in which there is not a significant change in elevation near the selected runway.
In addition to not providing a desired reaction time in instances in which the elevation of the terrain changes abruptly either at or near the selected runway, the terrain clearance floor envelope also does not necessarily provide alerts to the flight crew if the aircraft is below a predetermined minimum glideslope with respect to the selected runway. Specifically, with reference to FIG. 2, because the terrain clearance floor envelope is constructed based on the altitude of the aircraft with respect to underlying terrain and not based on the elevation of the selected runway, an aircraft that is above the terrain clearance floor envelope will not generate an alert even though the aircraft may be below the minimum glideslope that is recommended for the selected runway. As such, the flight crew will not be notified until shortly before reaching the runway that the aircraft is approaching the selected runway at an undesirably shallow angle, thereby leaving little time for the flight crew to adjust the landing pattern.
For each of these reasons, it would therefore be desirable to provide a ground proximity warning system that provides increased reaction time for abrupt changes in elevation near a selected runway and that provides timely alerts if the aircraft sinks below the minimum glideslope that is recommended for the selected runway, while also not unnecessarily increasing the number of nuisance alarms.
The apparatus, method and computer program product of the present invention therefore defines a runway field clearance floor envelope about a selected runway that represents different preselected altitudes above the selected runway at respective distances from the selected runway. By comparing the position of the aircraft to the runway field clearance floor envelope, an indication, such as an alarm, can be provided in instances in which the aircraft is positioned below the runway field clearance floor envelope. Since the runway field clearance floor envelope that is constructed by the apparatus, method and computer program product of the present invention is constructed relative to the runway by defining minimum altitude values that should be maintained relative to the elevation of the runway and not relative to the elevation of the terrain currently underlying the aircraft, the indications provided by the apparatus, method and computer program product of the present invention should provide the flight crew with ample reaction time in order to accommodate rather abrupt changes in elevation at or near a selected runway while not unnecessarily increasing the number of nuisance alarms. In addition, since the runway field clearance floor envelope oftentimes represents the minimum glideslope recommended for the selected runway, the apparatus, method and computer program product also provides the flight crew with a timely indication if the aircraft sinks below the minimum recommended glideslope.
In one embodiment, the apparatus, method, and computer program product compare a distance between the aircraft and the selected runway to the runway clearance floor envelope and determine a preselected altitude of the aircraft above the selected runway based upon the runway field clearance floor envelope. By comparing the preselected altitude to the actual altitude of the aircraft above the selected runway, an indication can be provided if the actual altitude of the aircraft above the selected runway is no more than the preselected altitude.
The runway field clearance floor envelope is preferably defined to have at least two boundaries. Moreover, at least one of the boundaries is preferably based on at least one of a runway position quality factor, an altitude data quality factor, and an aircraft position quality factor. As such, the apparatus, method and computer program product of the present invention determine the boundaries of the runway field clearance floor envelope based upon the uncertainties or, conversely, the quality with which the respective positions of the runway and the aircraft can be defined. For example, the inner boundary of the runway field clearance floor envelope can be defined proximate the selected runway by summing the runway position quality factor, altitude data quality factor, and aircraft position quality factor. In addition, an outer boundary of the runway field clearance floor envelope can be defined by summing the runway position quality factor, the altitude data quality factor, the aircraft position quality factor, and a predetermined outer distance representing a predetermined distance from the selected runway. As such, the outer boundary of the runway field clearance floor envelope will be displaced by the predetermined outer distance from the inner boundary. Moreover, the runway field clearance floor envelope can be further defined to have a preselected inner boundary altitude at the inner boundary and a preselected outer boundary altitude at the outer boundary, such that the resulting runway field clearance floor envelope has a corresponding slope therebetween.
In one embodiment, the position and elevation data for the selected runway are stored in a memory device. As such, the altitude of the aircraft above the selected runway can be determined by accessing the elevation data for the selected runway and subtracting the elevation of the selected runway from the actual altitude of the aircraft. In this regard, the altitude of the aircraft can be a calculated geometric altitude representing the altitude of the aircraft above sea level.
In addition to constructing the runway field clearance floor envelope, the apparatus, method and computer program product of one embodiment of the present invention can also define a terrain clearance floor envelope about the selected runway representing different preselected minimum altitudes of the aircraft above the currently underlying terrain at different distances between the aircraft and the selected runway. In this embodiment, the altitude of the aircraft above the underlying terrain at its current position can be compared to the corresponding minimum altitude defined by the terrain clearance floor envelope. If the aircraft falls or dips below the terrain clearance floor envelope, as indicated by the altitude of the aircraft above the terrain being no more than the minimum altitude defined by the terrain clearance floor envelope, an additional indication or alarm can be provided. Preferably, a ground proximity alert is generated if the aircraft falls below either the runway field clearance floor envelope or the terrain clearance floor envelope for more than the predetermined time. In this regard, if the aircraft falls below the runway field clearance floor envelope for more than the predetermined time, the altitude value that would otherwise indicate the altitude of the aircraft above the selected runway can be increased by a predetermined amount. As such, the aircraft must decrease in altitude by the predetermined amount before the next ground proximity alert will be generated. Likewise, if the aircraft falls below the terrain clearance floor envelope for more than the predetermined time, the altitude of the aircraft can be increased by a selected amount. As such, the aircraft must decrease in altitude by the selected amount before the next ground proximity alert will be generated.
The apparatus, method and computer program product of the present invention therefore provides a mechanism for detecting rather abrupt changes in elevation near a selected runway sufficiently far in advance that the flight crew is provided with ample time to make any necessary changes in the flight path. As described, the apparatus, method and computer program product of the present invention typically do not replace the terrain clearance floor envelope that has been traditionally generated about a selected runway. Instead, the apparatus, method and computer program product of the present invention generate an additional runway field clearance floor envelope.
As such, the apparatus, method and computer program product of the present invention also significantly increase protection, especially in those instances in which the terrain abruptly changes at or near an selected runway, by providing an alert either if the aircraft does not remain at an altitude sufficiently above the elevation of the runway or if the aircraft does not remain at a sufficient elevation above the currently underlying terrain.